Method and apparatus for detecting extraneous matter in a fluid

ABSTRACT

A method for detecting extraneous matter in a fluid including the steps of applying an energy source to electrodes located in a fluid, measuring real and imaginary electrical impedance values across the electrodes for a plurality of different frequencies of alternating energy and identifying at least one characteristic of an extraneous matter in the fluid.

FIELD OF THE INVENTION

[0001] The present invention relates to analysis of fluids such as oil.The invention is particularly concerned with monitoring fluid qualityfor extraneous matter such as contaminants.

BACKGROUND OF THE INVENTION

[0002] It has been estimated that the repairs and down time caused byoil-related engine or other machine failures represent about 30-50% ofthe operation cost in Australian mining industry. In the economies ofdeveloped countries the damage from machine and engine wear representsabout 6% of the gross national product. Thus, the development ofeffective techniques for the reliable prognosis of wear and maintainingthe effectiveness of working lubrication oils is of substantialinterest. Current diagnostic tests based on Scheduled Oil Sampling cannot promptly detect a rapidly progressing component failure or a suddeningestion of oil contaminants.

[0003] Furthermore, in many situations the timing of any oil change isassociated with the measured use of the vehicle or machine using the oilrather than the actual condition of the oil. Ideally it would bedesirable to monitor the condition of the oil so that information can beobtained about deterioration or contamination in the oil before anycatastrophic failure of the machine or machine components can takeplace.

[0004] Different methods have been adopted for monitoring the conditionof oil. For example, the specification of U.S. Pat. No. 4,831,362discloses an apparatus for detecting ferromagnetic particles inlubricating oil. The apparatus consists of two windings inductivelycoupled via the lubricating oil. A permanent magnet located behind asensor winding generates a magnetic flux which attracts ferromagneticparticles giving rise to pulses in the sensor winding.

[0005] U.S. Pat. No. 5,262,732 describes a system which utilises both apermanent magnet and electro magnet to simultaneously impose theirmagnetic fields upon the lubricating oil so as to attract ferromagneticparticles in the oil.

[0006] U.S. Pat. No. 6,204,656 discloses an array of sensors inconjunction with a magnetic field intensity gradient to obtain aparticulate distribution of ferrous particles across the array.Unfortunately, the systems of both of these patents are sensitive tomechanical vibration commonly encountered in moving machines.Furthermore, only limited information can be obtained about degradationof the oil which is being monitored.

[0007] Other systems have also been devised for monitoring oilcontamination, such as those that measure dielectric constant. However,there is no system which is currently able to monitor a range of oilcontaminants and which may be applicable to analysis and monitoring ofother fluids.

SUMMARY OF THE INVENTION

[0008] The present invention relates to a method and assembly fordetecting extraneous matter in a fluid. According to one embodiment ofthe invention an on-line detection system for lubrication oils isprovided based on an Electrical Impedance Spectroscopy technique. Thisdetector system is capable of providing on-line information on the typeand extent of contaminants and oil degradation, particularly theconcentration and average size of ferrous wear particles. Theinformation may enable an early detection of problems before they leadto costly repairs and down time.

[0009] According to one aspect of the present invention there isprovided a method for detecting extraneous matter in a fluid includingthe steps of applying an energy source to electrodes located in a fluid,measuring real and imaginary electrical impedance values across theelectrodes for a plurality of different frequencies of energy andidentifying at least one characteristic of at least one type ofextraneous matter in the fluid based on changes in the real andimaginary electrical impedance measured for the plurality of differentfrequencies.

[0010] It is preferred that the method is able to detect the type andlevel of extraneous matter in a fluid and to identify the type and/orlevel of extraneous matter in the fluid.

[0011] It is preferred that the energy source provides an alternatingcurrent or voltage to the electrodes.

[0012] The electrodes may be configured in one or more pairs so as toprovide a voltage drop across the pairs of electrodes.

[0013] It is preferred that the electrodes are configured with aplurality of first electrodes connected together and a plurality ofsecond electrodes connected together.

[0014] Real and imaginary impedance values preferably include real andimaginary components of mathematically related parameters such asimpedance, admittance, modulus and dielectric permittivity, etc.

[0015] Preferably the method includes identifying one or more featuresof extraneous matter present in the fluid.

[0016] The extraneous matter preferably includes matter such as gas,solid, liquid or energy such as heat, electric charge, etc or differentcombinations of the above.

[0017] According to one embodiment, the invention involves measuring thereal and imaginary parts of the impedance at a selected frequency orover a frequency range of 0.1 Hz to 1 MHz.

[0018] The measuring step may include displaying a frequency spectrumfor the real and imaginary parts of the impedance.

[0019] It is preferred that the method includes the step of measuringtemperature of the fluid at each measurement frequency or measuredimpedance spectrum.

[0020] The method may include the step of displaying and/or producing afrequency spectrum for the real and imaginary impedance values.

[0021] The method may include the step of displaying an impedancespectrum in the form of a complex plane plot of imaginary vs. realimpedance values or in the plotting of quantities derived from the realand imaginary impedance values.

[0022] Preferably the method includes the step of determiningconcentration and/or average particle size of ferrous wear particles.

[0023] It is preferred that concentration and/or size of ferrous wearparticles is determined from the impedance spectrum.

[0024] The frequency range is preferably between 0.1 Hz and 1 MHz.

[0025] The method may include the step of determining the extraneousmatter from the impedance spectrum measured.

[0026] Preferably the method includes the step of determining the numberof peaks and/or position of peaks in the measured impedance spectrum.

[0027] It is also preferred that the method includes the step ofdetermining the height of peaks and/or the relative height of peaks inthe measured impedance spectrum.

[0028] The method may include the step of measuring the impedancespectrum over a predetermined period of time.

[0029] According to one embodiment, the method includes the step ofmeasuring the impedance at a selected frequency over a period of time.

[0030] The method preferably includes the step of analysing theimpedance spectrum and producing a graph of impedance spectrum peakheight versus degree of extraneous matter such as oxidation degree.

[0031] It should be noted that reference to impedance spectrum refers toEIS (Electrical Impedance Spectrum).

[0032] The extraneous matter preferably includes soot, water, coolant,diesel, ferrous particles, oxidation products.

[0033] It is preferred that the method includes measurement from the EISof matter concentration and size, type of fluid etc.

[0034] It is preferred that the method includes the step of applying amagnetic field to attract ferrous particles between the electrodes,whereby the gap between the electrodes is able to be filled by a packedbed of the ferrous particles.

[0035] Preferably the magnetic field is generated using a DCelectromagnet.

[0036] The method may include measuring electrical impedance at aselected frequency across the packed bed of ferrous particles in the gapbetween the electrodes for a period of time.

[0037] The method may include providing a graphical display of one ormore characteristics of extraneous matter measured in the fluid.

[0038] Preferably the particle concentration is determined from the rateof change of impedance in the gap between the electrodes.

[0039] The method may include providing a first and second set ofelectrodes, the first set for detecting ferrous particles and the secondset for detecting other extraneous matter.

[0040] The method preferably includes providing a magnetic fieldgeneration means for generating a magnetic field through a region inwhich the first set of electrodes is located.

[0041] The magnetic field is preferably applied by a DC electromagnet.

[0042] The first set of electrodes may be mounted to a non-conductivesubstrate which is perpendicular to the axis of the magnet.

[0043] The size of the first set of electrodes is preferably muchsmaller than the second set of electrodes.

[0044] A first set of electrodes is preferably aligned axially to theflow of fluid down stream of the second set of electrodes.

[0045] Preferably the method includes the step of analysing theimpedance spectrum using pattern recognition algorithms to identify thetype and/or level of extraneous matter in the fluid.

[0046] Preferably the method includes the step of determining whether aparticular matter is present in the fluid by determining the change ofcharacterization parameters of the impedance spectrum.

[0047] According to another aspect of the present invention there isprovided an assembly for detecting extraneous matter in a fluidcomprising a first set of electrodes located in a fluid chamber, theelectrodes being aligned axially with the flow of fluid through thefluid chamber, a measuring device connected to the electrodes formeasuring real and imaginary impedance values across the electrodes fora plurality of frequencies, whereby a data processor is able to displaychanges in the real and imaginary impedance values for the plurality ofdifferent frequencies.

[0048] It is preferred that the measuring device is adapted to measurethe electrical impedance spectrum across the electrodes.

[0049] It is preferred that the apparatus includes a second set ofelectrodes located in the fluid chamber and connected to the measuringdevice for detecting a different extraneous matter to that detected bythe first set of electrodes.

[0050] The first set of electrodes is preferably located downstream ofthe second set of electrodes.

[0051] The assembly may include a magnetic field generator such as anelectromagnet.

[0052] The assembly preferably includes an adaptor housing with a fluidchamber in which the electrodes are located.

[0053] It is preferred that the method includes the step of determiningwhether a particular matter is present in the fluid by determining thechange of characterisation parameters, such as first and second autoderivatives, average values of imaginary impedance component over aselective range of real impedance, and etc. extracted from the measuredimpedance spectrum.

[0054] Preferably the step of calculating the rate of impedance decreasefrom the average slope of the curve of relative impedance vs. time inthe initial 50 seconds starting from when the magnetic field is appliedto the first set of electrodes.

[0055] It is preferred that the method includes recording a curve ofimpedance magnitude versus time and converting the curve into a curve ofrelative impedance, which is defined as the ratio of impedance magnitudeto the impedance magnitude without any ferrous particles in the gap,versus time.

[0056] According to a further aspect of the present invention there isprovided a method of analysing extraneous matter in a fluid includingthe steps of receiving impedance data, being data including real andimaginary impedance values measured across electrodes located in afluid, recording the impedance spectrum at a plurality of timeintervals, calculating the peak height of the impedance spectrum for thereceived impedance data, comparing the peak height of the impedancespectrum with a reference impedance spectrum peak height and determininga feature of the extraneous matter from the comparing steps.

[0057] The method preferably includes determining how many peaks arepresent in the impedance spectrum of the received data.

[0058] The method may include the step of determining whether aparticular matter is present by the number of peaks in the impedancespectrum and the height of the or each peak.

[0059] Preferably the method includes the step of determining whether aparticular matter is present by determining the height of a single peakor the impedance spectrum and determining whether this is within apredetermined range such as 30 to 50 KΩ.

[0060] The range of 30 to 50 KΩ may change as the configuration of theelectrodes changes.

[0061] It is preferred that the data processor is programmed to displaythe change of impedance magnitude over a period of time.

[0062] The method may include the step of determining whether aparticular matter is present by determining if the or each peak of theimpedance spectrum is deformed and has a significant tail.

[0063] The method may include the step of determining whether aparticular matter is present by determining if the or each peak of theimpedance spectrum is deformed and has a significant tail in a range oflow frequency.

[0064] Accordingly, the present invention provides a method of detectingcontamination in a fluid, the method including:

[0065] applying an electric field to an electrode pair supported withina fluid and measuring changes in field characteristics between the fluidand an uncontaminated sample of the same fluid.

[0066] The method may also include applying a magnetic field to thefluid in the vicinity of the electrode pair in order to attract ferrousparticles to the electrode pair.

[0067] The present invention also provides apparatus for detectingcontaminants in a fluid, the apparatus including an electrode pairsupported on a non-conductive base for emersion in a fluid,

[0068] means for applying an electric field to the electrodes, and

[0069] measuring means for measuring changes in field characteristics.

[0070] The apparatus may also include means for applying a magneticfield in the vicinity of the electrode pair.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Preferred embodiments of the present invention will now bedescribed by way of example only with reference to the accompanyingdrawings in which:

[0072]FIG. 1 shows a schematic diagram of an assembly for detectingextraneous matter in a fluid according to a first embodiment of thepresent invention;

[0073]FIG. 2 shows an impedance spectrum showing imaginary impedanceversus real impedance for a range of frequencies from 0.1 Hz to 1 MHz inaccordance with the first embodiment of the invention;

[0074]FIG. 3 shows a graphical representation of an impedance spectrumfor oil having water contamination according to a second embodiment ofthe invention;

[0075]FIG. 4 shows a graphical representation of an impedance spectrumaccording to a third embodiment of the present invention;

[0076]FIG. 5 shows a graphical representation of an impedance spectrumaccording to a fourth embodiment of the present invention;

[0077]FIG. 6 shows a graphical representation of an impedance spectrumaccording to a fifth embodiment of the present invention;

[0078]FIG. 7 shows a graphical representation of oxidation degree(allowable %) versus EIS Peak Height (ohms×10⁴) in accordance with asixth embodiment of the present invention;

[0079]FIG. 8 shows an impedance spectrum according to a seventhembodiment of the present invention;

[0080]FIG. 9 shows a schematic diagram of a method for detecting andanalysing extraneous matter in a fluid according to one embodiment ofthe present invention;

[0081]FIG. 10a shows a graphical representation of impedance vs. timebetween particle detecting electrodes reaching a limiting value when thegap is fully filled with ferrous particles, in accordance with oneembodiment of the invention.

[0082]FIG. 10b shows a graphical representation of impedance versus timeacross electrodes in a fluid according to one embodiment of the presentinvention;

[0083]FIG. 11 shows a graphical representation of rate of impedancedecrease versus iron particle concentration in accordance with oneembodiment of the present invention;

[0084]FIG. 12 shows a graphical representation of an impedance spectrumfor varying iron particle size in accordance with one embodiment of theinvention; and

[0085]FIG. 13 shows an adaptor for housing the assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0086] It should be noted that values of impedance shown in the Figuresare given in ohms.

[0087] As shown in FIG. 1 an assembly for detecting extraneous matter ina fluid consists of a set of fluid measurement electrodes 11 typicallyspaced 1.6 mm apart and a set of ferrous wear particle detectionelectrodes 12 typically 0.6 mm apart. These electrodes are located in afluid stream in an adaptor housing 13 as shown in FIG. 13.

[0088] The fluid measurement electrodes 11 are much larger than theferrous particle detection electrodes 12 and are located upstream of theferrous particle detection electrodes 12.

[0089] The ferrous particle detection electrodes 12 are also aligned inparallel at right angles together to the axis of alignment of the fluidmeasurement electrodes 11.

[0090] The ferrous particle detection electrodes being much smaller thanthe fluid measurement electrodes 11 are located in a smaller fluidchamber 14 of the adaptor 13.

[0091] A DC electromagnet 18 is located in close proximity to the fluidchamber 14 so as to provide a magnetic field through this chamber.

[0092] The other chamber 15 in which the fluid measurement electrodesare provided is preferably isolated from the chamber 14.

[0093] Each set of electrodes consists of successive pairs of electrodeswith alternate electrodes of each pair electrically connected together.

[0094] An electrical impedance spectrometer 16 is connected to each ofthe sets of electrodes as well as to a data processor such as a minicomputer 17.

[0095] In operation oil flows through the adaptor 13 and passes betweenthe plates of the fluid measurement electrodes 11 and the ferrous wearparticle detection electrodes 12.

[0096] By energising the electromagnet or solenoid 18 a magnetic fieldis established through chamber 14.

[0097] The electrical impedance spectrometer 16 is then operated torecord the electrical impedance across the electrodes 12 at a selectedfrequency typically 10 kHz.

[0098] Under the effects of the magnetic field ferrous wear particles inthe oil such as lubrication oil will be moved into the gap between theelectrodes. Over a period of time ferrous particles will gradually fillthe gap between each pair of electrodes and finally the electrodes 12will be completely buried in a pile of ferrous particles. Therefore,over a period of time the impedance across each pair of electrodes willgradually decrease until the impedance is approaching a limiting valueas shown in FIG. 10a.

[0099] The higher the concentration of ferrous particles the shorter thetime interval between a limiting value of the impedance across theelectrodes 12 is approached.

[0100] Due to the enrichment effect of the magnetic field and the use ofa narrow gap between each pair of electrodes the assembly is able todetect iron particles with a concentration as low as a few parts permillion.

[0101] By using a number of pairs of electrodes as in FIG. 1 thesensitivity of the assembly is increased further.

[0102] The use of a strong magnetic field allows most of the ferrousparticles, including the size range of 5 to 20 micrometers, to travelfrom the bulk oil phase into the gap between the electrodes.

[0103] As shown in FIG. 10b the effect of concentration of iron(ferrous) particle on the measured relative impedance decreases withtime during the time of ferrous particles having the size range 63 to102 micrometers accumulate in the gap between the electrodes. Therelative impedance is defined as the ratio of the impedance in the gaphaving the action of magnetic field to that without any ferrousparticles in the gap. Thus FIG. 10b shows how the impedance in the gapbetween electrodes 12 for the case with the higher ferrous particleconcentration, for example 200 parts per million (PPM) decreases fasterthan those for lower ferrous particle concentration.

[0104] The effect of iron particle concentration and size on the rate ofimpedance decrease is shown in FIG. 11. The rate of impedance decreaseis defined as the average slop in the initial 50 seconds of theimpedance decrease curve, as shown in FIG. 10b. From this figure it canbe seen how the larger particle size has a greater rate of impedancedecrease for a particular iron particle concentration.

[0105] In FIG. 12 the effect of iron particle size on EIS of packed bedin the fully filled gap between the detecting electrodes 12 is shown. Itcan be seen that for each iron particle size there is a peak imaginaryimpedance value, which decreases with an increase in particle size.

[0106] The position of the imaginary impedance peak also varies inrelation to the real impedance value for different iron particle sizes.

[0107] From the above it can be seen that by observing the electricalimpedance spectrum it is possible to identify size and concentrationattributes of iron or ferrous particles in a fluid such as oil.

[0108] Before starting the next measurement cycle, the electromagnetshould be switched off to release the ferrous particles attracted in thegap between the first set of electrodes. A new measurement is started byswitching on the electromagnet and immediately followed by measuring andrecording the magnitude of impedance in the gap as a function of time.Recording is stopped when the impedance magnitude reaches a limitingvalue or changes very slowly with time. Then the electrical impedancespectrum across the fully filled gap is determined by measuring real andimaginary electrical impedance values for a plurality of differentfrequencies of alternating energy. Characterization parameters,including the peak height, impedance magnitude or real and imaginarycomponent values at selected frequencies are determined from theelectrical impedance spectrum and compared with those referenceparameters stored for different ferrous particle sizes so as todetermine the size of ferrous particles in the gap. The curve ofimpedance magnitude vs. time is converted into a curve of relativeimpedance vs. time by dividing the impedance magnitude with that withoutany ferrous particles in the gap. The rate of impedance decrease is thencalculated from the average slop of the curve of relative impedance vs.time in the initial 50 seconds. The rate of impedance decrease iscompared with reference rate of impedance decrease stored for differentferrous particle sizes so as to determine the concentration of ferrousparticles in the fluid.

[0109] Because fluid such as oil includes other contaminants thanferrous particles, the assembly shown in FIG. 1 includes the largerelectrodes 11.

[0110] By measuring the electrical impedance spectrum across the fluidmeasurement electrodes 11, information about extraneous matter in thefluid can be identified.

[0111] For example as shown in FIG. 2 the effects of oil type/brand onelectrical impedance spectrum of fresh lubrication oils can beascertained.

[0112] For a frequency range of 0.1 Hz to 1 MHz different types of oilsrepresented by references 20, 21, 22, 23, 24 can be obtained. In eachcase the impedance spectrum produces a peak imaginary impedance value ata particular frequency which drops off on either side of the peak. Thisgraphical or corresponding mathematical representation of the spectratherefore provides a reference curve for particular types of fluids (inthis case oils). These reference curves can be established for a rangeof temperature points.

[0113] In order to identify extraneous matter such as gases, oxidates,soot etc. the EIS can be observed to identify extraneous matter such ascontaminants in the fluid.

[0114] Therefore as shown in FIG. 3 the EIS for oil having watercontamination is shown.

[0115] For oil having 0.5% water contamination the impedance spectrumstill exhibits a peak but this peak drops off with decreasing frequencyvalue to a stepped region 25 before tailing off through region 26. Asthe amount of water contamination increases (2% water) the EIS spectrumproduces two peaks 27, 28. By observing the number of peaks, theirheight and their position it is therefore possible to identify whetherwater is a contaminant.

[0116] In FIG. 4 an EIS is produced for oil having coolant (ethyleneglycol) as a contaminant. In this case for a 0.1% coolant a curve isproduced having two peaks of different heights. As the coolantcontaminant increases (0.5% coolant) in percentage terms the second peakreduces in size relative to the first peak as referenced by item 29 and30.

[0117] Depending upon the type of oil the shape of the peaks and thedifference in height will vary. Thus for some oils contaminated withwater or a coolant, the second peak may be greater in height than thefirst peak. However, by using the uncontaminated EIS curve and comparingthis with EIS curves for different amounts of water or coolantcontaminant it is possible to identify the amount of water or coolant bycomparing a detected EIS curve with prerecorded data showing EIS curveswith different water or coolant contamination and matching the detectedEIS curve in a field application with the prerecorded EIS curves toobtain a best estimate of the amount of water or coolant contamination.

[0118]FIG. 5 shows another example of EIS curves for an oil having adiesel contaminant. Curve 31 shows the uncontaminated oil curve whereascurve 32 shows the contaminated oil curve.

[0119] By obtaining data on how the EIS curves change with dieselcontamination it is possible to produce a data base which can be used areference point for any field testing of oils for diesel contamination.

[0120]FIG. 6 shows the EIS change of oil with usage time in hours. Itcan be seen that for this particular oil the peak imaginary impedancevalue increases with usage time till 200 hours then decreases. For otheroils the peak values can always decrease with usage time.

[0121] In FIG. 7 a graphical representation is provided of how the EISpeak height in its decreasing stage as shown in FIG. 6 gives anindication of the oxidation degree in allowable percentage. Similarrelationship for the peak height increasing stage can be alsoestablished. Therefore by observing the peak height of an EIS curve itis possible for a particular oil to identify the degree of oxidation.

[0122] In FIG. 8 the shape and height of the peak of the EIS curvevaries according to soot content. The curves show how the peak isdeformed and tails off more with increasing soot content.

[0123] Based on observations derived from EIS measurements taken usingthe aforementioned detection assembly it is possible to employ anautomated procedure to identify extraneous matter in oil. This automatedprocedure which may be implemented by a computer program is describedwith reference to FIG. 9.

[0124] Once an oil change has occurred referenced by item 40 theelectrical impedance spectrum is measured for a range of temperaturepoints and recorded using the aforementioned detection apparatus. If theoil type/brand is right for the particular application as referenced byitem 41 a controlling computer is able to activate the detectionapparatus so as to measure and record the EIS say every 5 minutes asreferenced by item 42. Alternatively if the right type of oil has notbeen provided an alarm signal is provided to a display to notify anobserver that the right type of oil needs to be used.

[0125] After the EIS has been measured and recorded the data processoris programmed to calculate the number of peaks and the peak height andcharacterise the peak shape for each curve produced as referenced byitem 43. Then data processor performs data analysis to identify whetherthe EIS has dual peaks as referenced by item 44. If the answer is yesthe data processor is programmed to identify whether the height of thepeaks is less than a predetermined threshold, for example 30 kΩ, asidentified by item 45. If it is then the data processor is able toproduce an output indicating that water or coolant contamination hasbeen identified in the oil, as referenced by item 46. Alternatively ifthe height is greater than the predetermined threshold an output isproduced by the data processor, as referenced by item 47 which indicatesthat there is diesel fuel contamination. Returning to item 46 if in thealternative the data processor identifies that the EIS does not havedual peaks it performs a comparison step as referenced by item 48, inwhich the height of the EIS curve measured is compared with those in thebase or reference EIS as well as the previous EIS. If the height isgreater than both the reference EIS and the EIS from the previousmeasurement the data processor records this and continues to instructthe detection assembly to measure and record EIS every five minutes. Inthe alternative if the height is lower than that in the reference EIS orthe previous one an additional analysis step is performed in item 49. Ifthe height of the EIS is lower than the previous EIS then an additionalanalysis is performed by the data processor to identify whether theheight of the peak is in a predetermined range, for example 30 to 50 kΩ,as identified by item 50. If the data processor identifies that theheight is within this range it produces an output, as referenced by item51 indicating that high oxidation and sulfur products could be the causeof the contamination.

[0126] If the height is not in a predetermined range the data processoranalyses the peak to identify whether it is deformed and contains asignificant tail, as represented by item 52. If the data processoridentifies there is sufficient deformation an output is producedindicating that there is soot contamination, as identified by reference53.

[0127] If there is no peak deformation then the data processor deducesthat the oil is not heavily contaminated by any of the previouslymentioned contaminants and continues to measure and record EIS inaccordance with item 42. Likewise if the height of the peak is lowerthan the last one as in item 45 the measurement and recording step ofitem 42 is repeated.

[0128] The above procedure can be implemented by using the detectorassembly as shown in FIG. 1 with the mini computer 17 appropriatelyprogrammed to control the electrical impedance spectrometer to take EISmeasurements and to then analyse the EIS results.

[0129] It is also possible for the detection assembly to be controlledon-line by remote telemetry for example.

[0130] According to another embodiment of the invention the detectionassembly can be modified to combine the electrodes into a single bank ofelectrodes so as to combine detection of iron particles with otherextraneous matter.

[0131] Although the preferred embodiment of the invention has beendescribed utilising an electronic impedance spectrometer, alternativedevices may be used to record real and imaginary impedance values over arange of frequencies. For example a voltage source could be utilisedhaving a variable frequency. An amp meter could then be utilised tomeasure the change in current. Alternatively an oscilloscope could beutilised to record the impedance spectrum.

What is claimed is
 1. A method for detecting extraneous matter in afluid including the steps of: applying an energy source to electrodeslocated in a fluid; measuring real and imaginary electrical impedancevalues across the electrodes for a plurality of different frequencies ofalternating energy; and identifying at least one characteristic of anextraneous matter in the fluid based on changes in the real andimaginary electrical impedance measured for the plurality of differentfrequencies.
 2. The method as claimed in claim 1 wherein the energysource provides an alternating voltage to the electrodes.
 3. The methodas claimed in claim 1 wherein electrodes are configured with a pluralityof first electrodes connected together and a plurality of secondelectrodes connected together.
 4. The method as claimed in claim 3wherein the measuring step includes displaying an impedance spectrum inthe form of a complex plot of real parts of impedance versus imaginaryparts of impedance.
 5. The method as claimed in claim 4, including thestep of comparing the impedance spectrum measured with a referenceimpedance spectrum to determine a feature of extraneous matter presentin the fluid.
 6. The method as claimed in claim 5 including the step ofdetermining at least one type of extraneous matter present in the fluidfrom a comparison of the measured impedance spectrum relative to areference impedance spectrum for the fluid without extraneous matterpresent.
 7. The method as claimed in claim 6 wherein the frequencyspectrum is measured in the range of 0.1 Hz to 1 MHz.
 8. The method asclaimed in claim 7 including the step of determining the number of peaksin themeasured impedance spectrum and determining from the or each peakwhether a particular extraneous matter is present in the fluid.
 9. Themethod as claimed in claim 7 including the step of determining theheight of each peak in the impedance spectrum and comparing the heightof each peak measured to the height of one or more of the peaks in areference impedance spectrum for the fluid without extraneous matter soas to determine a type of extraneous matter present in the fluid. 10.The method as claimed in claim 9 including the step of determiningwhether the height of a peak measured in the impedance spectrum iswithin a predetermined range.
 11. The method as claimed in claim 10including the step of analysing the impedance spectrum measured toidentify whether a peak is present which is deformed and contains asignificant tail, so as to determine if extraneous matter in the form ofsoot is present in the fluid.
 12. The method as claimed in claim 11including the step of analysing the impedance spectrum using patternrecognition algorithms to identify the type and/or level of extraneousmatter in the fluid.
 13. The method as claimed in claim 1, including thestep of applying a magnetic field across at least one pair of electrodesso as to attract ferrous particles between the electrodes.
 14. Themethod as claimed in claim 13 including the step of storing referenceimpedance spectra for the fluid for particular extraneous matter. 15.The method as claimed in claim 14 including the step of comparing themeasured real and imaginary electrical impedance values with referencereal and imaginary electrical impedance values stored for the fluid inmemory and outputting the type of extraneous matter present in the fluidif the impedance spectrum measured is substantially the same as one ofthe impedance spectra stored in memory.
 16. The method as claimed inclaim 13 including the step of providing a first and second set ofelectrodes, the first set for detecting ferrous particles and the secondset for detecting other extraneous matter.
 17. The method as claimed inclaim 16 including the step of providing a magnetic field generationmeans for generating a magnetic field through a region in which thefirst set of electrodes is located.
 18. An assembly for detectingextraneous matter in a fluid comprising: a first set of electrodeslocated in a fluid chamber, the electrodes being aligned axially withthe flow of fluid through the fluid chamber; and a measuring deviceconnected to the electrodes for measuring real and imaginary impedancevalues across the electrodes for a plurality of frequencies, whereby adata processor is able to display changes in the real and imaginaryimpedance values for the plurality of different frequencies.
 19. Theassembly as claimed in claim 18 including a second set of electrodeslocated in the fluid chamber and connected to the measuring device formeasuring a different extraneous matter to the first set of electrodes.20. The assembly as claimed in claim 19 wherein the first set ofelectrodes is located downstream of the second set of electrodes. 21.The assembly as claimed in claim 20 including an adaptor housing with afluid chamber in which the electrodes are located.
 22. A method ofanalysing extraneous matter in a fluid including the steps of: receivingimpedance data, the impedance data including real and imaginaryimpedance values measured across electrodes located in a fluid;recording the impedance spectrum at a plurality of time intervals;calculating the peak height of the impedance spectrum for the receivedimpedance data; comparing the peak height of the impedance spectrum witha reference impedance spectrum peak heights; and determining a featureof the extraneous matter from the comparing step.
 23. The method asclaimed in claim 22 including the step of determining how many peaks arepresent in the electrical impedance spectrum of the received impedancedata.
 24. The method as claimed in claim 23 including the step ofdetermining whether a particular matter is present by the number ofpeaks in the electrical impedance spectrum and the height of one or moreof the peaks.
 25. The method as claimed in claim 23 including the stepof determining whether a particular matter is present by determining ifthe peak of the electrical impedance spectrum is deformed and has asignificant tail.
 26. The method as claimed in claim 23 including thestep of determining whether a particular matter is present bydetermining whether the height of a single peak is within apredetermined range of imaginary impedance values.
 27. The method asclaimed in claim 21 including the step of determining whether aparticular matter is present in the fluid by determining the change ofcharacterisation parameters.
 28. A method for detecting a characteristicof ferrous particles in a fluid including the steps of: applying amagnetic field to fluid in the vicinity of a first set of electrodes toattract ferrous particles into a gap between the electrodes; measuringthe magnitude of the impedance across the electrodes as a function oftime until the gap is bridged by ferrous particles; measuring real andimaginary electrical impedance values across the electrodes for aplurality of different frequencies of alternating energy; andidentifying at least one characteristic relating to ferrous particles.29. The method as claimed in claim 28 wherein the characteristicrelating to ferrous particles includes one of the size and concentrationof ferrous particles.
 30. The method as claimed in claim 29 includingthe step of removing the magnetic field when the ferrous particlesbridge the gap, whereby ferrous particles are released into the fluidbefore starting a next measuring step.
 31. The method as claimed inclaim 30 including the step of recording the measured magnitude ofimpedance across the gap between the first set of electrodes as afunction of time and determining whether the gap is fully filled withferrous particles by observing whether the impedance magnitude reaches alimiting value or changes very slowly with time.
 32. The method asclaimed in claim 30 including the step of recording a curve of impedancemagnitude vs. time and converting the curve into a curve of relativeimpedance.
 33. The method as claimed in claim 32 including the step ofcalculating the rate of impedance decrease from the average slope of thecurve of relative impedance vs. time in the initial 50 seconds startingfrom when the magnetic field is applied to the fluid.
 34. The method asclaimed in claim 33 including the steps of: determining one or morecharacterising parameters of the ferrous particles from the peak height,impedance magnitude or real and imaginary component values at selectedfrequencies, or from the impedance spectrum measured in the fully filledgap between the first set of electrodes; and comparing one or more ofthe characterizing parameters with those reference parameters stored fordifferent ferrous particle sizes so as to determine the size of ferrousparticles in the gap.
 35. The method as claimed in claim 34 includingthe step of comparing the rate of impedance decrease with reference rateof impedance decrease stored for different ferrous particle sizes so asto determine the concentration of ferrous particles in the fluid. 36.The method as claimed in claim 3 including the step of measuring thereal and imaginary parts of impedance over a frequency range of 0.1 Hzor 1.0 MHz and displaying an impedance spectrum in the form of thecomplex plane plot of imaginary vs. real impedance values.
 37. Themethod as claimed in claim 3 wherein the measuring step includes:measuring the real and imaginary parts of impedance over a frequencyrange of 0.1 Hz to 1.0 MHz; and displaying an impedance spectrum by theplotting of quantities related to the real and imaginary impedancevalues.
 38. The method as claimed in claim 37 including the step ofextracting measured impedance spectrum parameters characterizing thespectrum pattern.